1. Field of the Invention
The present invention relates to a method and apparatus for providing a service, such as a multimedia broadcast/multicast service (MBMS), in a universal mobile telecommunications system (UMTS), and more particularly, to a method and apparatus for selecting a radio bearer type according to a count of mobile terminals obtained through responses to a service response request message from a network.
2. Discussion of the Related Art
The universal mobile telecommunications system (UMTS) is a third-generation mobile communications system evolving from the global system for mobile communications system, which is the European standard. The UMTS is aimed at providing enhanced mobile communications services based on the GSM core network and wideband code-division multiple-access technologies.
A conventional UMTS network structure 1 is illustrated in FIG. 1. One mobile terminal 2, or user equipment (UE), is connected to a core network 4 through a UMTS terrestrial radio access network (UTRAN) 6. The UTRAN 6 configures, maintains, and manages a radio access bearer for communications between the UE 2 and core network 4 to meet end-to-end quality-of-service requirements.
The UTRAN 6 consists of at least one radio network subsystem 8, including one RNC 10 acting as an access point to the core network, and at least one Node B 12 managed by a corresponding RNC. The RNCs 10 are logically classified as controlling RNCs, which allocate and manage common radio resources for a plurality of UEs 2 of a cell, and serving RNCs, which allocate and manage dedicated radio resources for a specific UE of a cell. Each Node B 12 manages at least one cell.
The core 4 network may be divided according to the type of service provided, namely, a circuit-switched (CS) domain and a packet-switched (PS) domain. The CS domain includes a mobile switching center (MSC) 14 acting as an access point to the UTRAN 6 and a gateway mobile switching center (GMSC) 16 acting as an access point to an external network. The PS domain includes a serving GPRS support node (SGSN) 18 acting as an access point to the UTRAN 6 and a gateway GPRS support node (GGSN) 20 acting as an access point to the external network.
In the CS domain, the core network's 4 access point is the MSC 14 via an Iu-CS interface. In the PS domain, the core network's 4 access point is the SGSN 18 via an Iu-PS interface. A visitor location register (VLR) 22 and a home location register (HLR) 24 manage user registration information.
The air interface (Uu) between the UE 2 and the UTRAN 6 includes a radio resource control (RRC) layer (not shown) for the establishment, reconfiguration, and release of radio bearers, for example a service providing data transfer between the UE and an RNC 10 of the UTRAN. A UE 2 is said to be in the RRC-connected mode when the RRC layer of a UE and the RRC layer of a corresponding RNC 10 are connected, thereby providing for bi-directional transfer of RRC messages. If there is no RRC connection, the UE 2 is said to be in the RRC-idle mode.
The serving RNC 10 of an RRC-connected UE 2 recognizes and manages the UE by cells. An RRC-idle UE 2, on the other hand, cannot be recognized by cells and can be considered invisible to the RNC 10. Therefore, the MSC 14 or SGSN 18 of the core network 4 manages RRC-idle UEs 2 using larger areas, such as location units or routing area units.
Upon power-up, a UE 2 is in the RRC-idle mode by default. When necessary, an RRC-idle UE 2 transitions to the RRC-connected mode through an RRC connection procedure.
An RRC connection is established, for example, when uplink data transfer is needed to make a call or to respond to a paging message from the RNC 10. The RRC connection connects the UE 2 to the RNC 10 of the UTRAN 6. However, in order to receive a service, for example MBMS, the UE must be connected to the core network 4 (MSC 14 or SGSN 18). Connection of the UE 2 to the core network 4 for control of the service is achieved by a “signaling connection,” either a CS connection or PS connection according to the type of service.
A CS connection, which is established between the UE 2 and MSC 14, consists of an RRC connection and an Iu-CS connection. When there is a CS connection, the UE2 is said to be in the circuit mobility management (CMM) connected, or CMM-connected, mode. When there is no such connection, the UE 2 is said to be in the CMM-idle mode.
A PS connection, which is established between the UE 2 and SGSN 18, consists of an RRC connection and an Iu-PS connection. When there is a PS connection, the UE 2 is said to be in the packet mobility management (PMM) connected, or PMM-connected, mode. When there is no such connection, the UE 2 is said to be in the PMM-idle mode.
One UE 2 may have two signaling connections, for example both a CS connection and a PS connection, but only one RRC connection. An RRC-connected UE 2 may have no signaling connection, whereby the UE is managed by the RNC 10 only and cannot receive services.
To join a specific MBMS, both an RRC connection and an Iu-PS connection, or a PS connection, is required through which a UE 2 is connected to the SGSN 18. An MBMS-joined UE 2 remains in the RRC-connected mode by maintaining the PS connection. Upon termination of the service, the UE 2 transitions to the RRC-idle mode by severing the PS connection.
When MBMS data transfer is eminent and a UE2 is standing by, for example intending to receive data of the MBMS, the SGSN 18 sends a “session start” message to the RNC 10. The RNC 10 transmits an MBMS notification message to the UE 2 at least once before the MBMS data is transferred.
The MBMS notification message is transmitted via a combination of common logical and transport channels. At the time of MBMS notification, the RNC 10 recognizes, or counts, the number of UEs 2 joining the MBMS within a cell. The counted number of UEs 2 determines whether a radio bearer will be established for providing a specific MBMS, and if so, whether the established radio bearer will be a point-to-multipoint (p-t-m) type or a point-to-point (p-t-p) type. Proper establishment of a radio bearer ensures efficient utilization of radio resources.
FIG. 2 illustrates a conventional connection of a plurality of UEs 2 to a core network 4 providing an MBMS. The RNC 10 first receives information from the SGSN 18 to determine the number of UEs 2 intending to receive the MBMS. Recognizing the presence of UEs 2 that join the MBMS and remain in the RRC-connected mode due to another service, the SGSN 18 provides the RNC 10 with information regarding PMM-connected UEs 2.
Specifically, the SGSN 18 provides “initial” UE 2 identification information, such as an intrinsic identifier or ID assigned to each UE, and the MBMS identification, or service ID information, of the specific service that the UE is joining. The RNC 10 stores the initial UE IDs of the UEs 2 joining the MBMS and thereby counts the number of RRC-connected UEs among a plurality of UEs joining the MBMS.
The initial UE ID enables the identification of a UE 2 regardless of its RRC connection status, thereby enabling identification of UEs by a core network 4 entity such as the MSC 14 or SGSN 18. The initial UE ID may be an international mobile subscriber identity (IMSI) enabling a subscriber's identification worldwide, a temporary mobile subscriber identity (TMSI) allocated by the MSC 14 to a UE 2 having a CS connection for security of the IMSI, or a packet TMSI allocated by the SGSN 18 to a UE having a PS connection.
Since RRC-idle UEs 2 are invisible to the SGSN 18, a UE having transitioned to the RRC-idle mode after joining the MBMS cannot be counted by the RNC 10 in the same manner as an RRC-connected UE. In order to count RRC-idle UEs 2, the RNC 10 receives an RRC-connection request message from each RRC-idle UE receiving an MBMS response request message via a combination of common logical and transport channels. The RRC-connection request message is transmitted by a UE to inform the RNC 10 of its presence using a combination of common logical and transport channels. The RRC-connection request message includes the service ID of the MBMS that the UE 2 intends to receive.
The RNC 10 adds the number of RRC-idle UEs 2 to the number of RRC-connected UEs, which is a number included in the PMM-connected UE information received from the SGSN 18, in order to determine the total number of UEs intending to receive the MBMS in each cell. The RNC 10 compares the total to a threshold. If the number of UEs 2 intending to receive the MBMS in a cell is less than the threshold, the RNC 10 establishes a p-t-p MBMS radio bearer. If the number of UEs 2 intending to receive the MBMS in a cell is greater than the threshold, the RNC 10 establishes a p-t-m MBMS radio bearer. No MBMS radio bearer is established for the cell if there is no UE 2 intending to receive the service.
After determining the appropriate MBMS radio bearer, the RNC 10 informs the UEs 2 accordingly. If a p-t-p MBMS radio bearer is established for a specific MBMS, each UE 2 intending to receive the service transitions to the RRC-connected mode. On the other hand, if a p-t-m MBMS radio bearer is established, it is unnecessary for all the UEs 2 to remain in the RRC-connected mode since MBMS data reception by RRC-idle UEs is enabled when a p-t-m radio bearer is established.
The RNC 10 informs the SGSN 18 of the established MBMS radio bearer. In transmitting MBMS data via the established MBMS radio bearer, the SGSN 18 first transmits the session start message, followed after a time interval by the MBMS data. The time interval is sufficient for the RNC 10, in response to the session start message, to send an MBMS notification to the UEs 2, to count the UEs, and to determine the MBMS radio bearer.
In performing the MBMS counting function to determine the appropriate MBMS radio bearer, an RNC 10 adopting the conventional method receives information regarding RRC-connected UEs. The number of RRC-idle UEs 2 is determined by the number of UEs that respond to an MBMS response request message with an RRC-connection request message.
However, not all RRC-idle UEs 2 in a cell intending to receive the MBMS need to transmit an RRC-connection request message. The conventional method cannot determine the number of UEs 2 in the RRC-connected mode and PMM-idle mode.
If a CS connection is established, for example for carrying out a voice communication function, by an MBMS-joined UE2 having transitioned to the RRC-idle mode to stand by for MBMS notification, an RRC connection exists but without a PS connection. In the conventional method, the RRC-connected but PMM-idle UE 2 is omitted from the RNC's 10 count since the SGSN 18 is unable to inform the RNC of the UE's presence.
An incorrect count of UEs 2 may be a serious problem if there are very few RRC-idle UEs among those joining an MBMS in a cell. A particular problem may occur if the number of RRC-idle UEs 2 is below the threshold for triggering a p-t-m radio bearer.
For example, if only one among a relatively large number of UEs 2 joining a specific MBMS within a cell stands by for MBMS notification in the RRC-idle mode and all others enter the RRC-connected mode to establish a CS connection, the RNC 10 is unable to recognize the majority of UEs since they are in the RRC-connected and PMM-idle mode. Since the RNC 10 counts only one UE 2 intending to receive the MBMS with the conventional method, a p-t-p radio bearer is established. A p-t-p radio bearer is an insufficient resource for the majority of the UEs 2 in the cell to receive the MBMS. In an extreme case, when every UE 2 of a cell is in the RRC-connected and PMM-idle mode, the RNC 10 would stop MBMS data transfer altogether since no UEs 2 intending to receive the MBMS would be counted using the conventional method.
Therefore, there is a need for a method and apparatus for accurately counting the number of mobile terminals in a cell that need to establish an RRC-connection to receive a specific service in order to properly determine the appropriate radio bearer needed. The present invention addresses these and other needs.